During IC fabrication, some processes subject the substrate to UV radiation (e.g., lithography). Exposure to UV radiation has been known to degrade some types of materials used to form the ICs. For example, ferroelectric materials used to form components such as ferroelectric capacitors of ferroelectric memory cells are sensitive to UV radiation.
FIG. 1 shows a conventional ferroelectric memory cell 105 having a transistor 130 and a ferroelectric capacitor 140. The capacitor comprises a ferroelectric ceramic thin film sandwiched between first and second electrodes 141 and 142. Electrode 142 is coupled to a plateline 170 and electrode 141 is coupled to the transistor which selectively couples or decouples the capacitor from a bitline 160, depending on the state (active or inactive) of a wordline 150 coupled to the transistor gate. A plurality of cells are interconnected by platelines, bitlines, and wordlines to form an array.
To realize high-density ICs, a capacitor over plug (COP) structure is employed. FIG. 2 shows a conventional ferroelectric COP structure 203. The COP structure is formed on a substrate 205 and insolated by an interlevel dielectric (ILD) layer 270. The COP structure includes a capacitor 240 having a ferroelectric layer 246 located between first and second electrodes 141 and 142. The first electrode is coupled to, for example, a diffusion region of a transistor via a plug 265 while the second electrode is coupled to a plateline via a contact formed in a contact hole 268.
To form the contact hole, a conventional lithographic process is used. Such lithographic process subjects the substrate to UV radiation. As shown, the ferroelectric material on the capacitor sidewalls is exposed, leaving it vulnerable to the UV radiation which can degrade its electrical properties.
From the foregoing discussion, it is desirable to provide a ferroelectric capacitor which avoids or reduces the adverse affects of UV radiation.